My 6 month old lab started off great with retrieving bumpers. Now once he retrieves the bumper he wants to play with it, I'll reel him in with the lead and he will push on the ground with the bumper in order to attempt to keep it. He only gets bumpers when training, after each session they are put up to the next. Is this something that should break on its own over time? Or are there steps I should follow to try to change this behavior? Any help is greatly appreciated, thanks in advance!